1. Field of the Invention
The present invention relates to reducing the risk of production and release of silica dust at a well site during fracking operation. More particularly, the invention relates to methods and systems to enhance transfer of proppant for hydraulic fracking operations from a container while reducing the risk of production and release of silica dust at a well site.
2. Description of Related Art
Hydraulic fracturing or “fracking” has been used for decades to stimulate production from conventional oil and gas wells. In recent years, the use of fracking has increased due to the development of new drilling technology such as horizontal drilling and multi-stage fracking. Such techniques reach previously-unavailable deposits of natural gas and oil. Fracking generally includes pumping fluid into a wellbore at high pressure. Inside the wellbore, the fluid is forced into the formation being produced. When the fluid enters the formation, it fractures, or creates fissures, in the formation. Water, as well as other fluids, and some solid proppants, are then pumped into the fissures to stimulate the release of oil and gas from the formation.
By far the dominant proppant is silica sand, made up of ancient weathered quartz, the most common mineral in the Earth's continental crust. Unlike common sand, which often feels gritty when rubbed between your fingers, sand used as a proppant tends to roll to the touch as a result of its round, spherical shape and tightly-graded particle distribution. Sand quality is a function of both deposit and processing. Grain size is critical, as any given proppant should reliably fall within certain mesh ranges, subject to downhole conditions and completion design. Generally, coarser proppant allows a higher capacity due to the larger pore spaces between grains. This type of proppant, however, may break down or crush more readily under stress due to the relatively fewer grain-to-grain contact points to bear the stress often incurred in deep oil- and gas-bearing formations.
Along with increased access to fossil fuels comes new and added challenges for the industry. Exposure to airborne silica has been identified by studies as a health hazard to workers conducting some fracking operations. These studies show that workers may be exposed to dust with high levels of respirable crystalline silica (“silica dust”) during fracking operations. See Eric J. Esswein, Michael Breitenstein, John Snawder, Max Kiefer & W. Karl Sieber (2013): Occupational Exposures to Respirable Crystalline Silica During Hydraulic Fracturing, Journal of Occupational and Environmental Hygiene, 10:7, 347-356. The National Institute for Occupational Safety (“NIOSH”) published a hazard alert along with OSHA relating to the health hazards particular to the fracking industry. The hazard alert explains that “[t]ransporting, moving, and refilling silica sand into and through sand movers, along transfer belts, and into blender hoppers can release dust containing silica into the air.”
Workers use many tons of proppant at a well site for fracking. These workers risk being exposed to silica dust, which, risks eventually leading to a disease called silicosis, or “Potter's Rot.” Silicosis is a form of occupational lung disease caused by inhalation of crystalline silica dust, and is marked by inflammation and scarring in the form of nodular lesions in the upper lobes of the lungs. It is a type of pneumoconiosis, or lung disease caused by the inhalation of dust, usually from working in a mining operation. This dust has other effects, such as contaminating the atmospheric air, creating a nuisance to adjacent landowners, and damaging equipment on the well site. Bloggers and environmental groups have taken a stand against hydraulic fracturing, in part, because of the silica dust created at the well site.
Throughout the process of delivering, blending, and mixing proppant at a well site, there is substantial production and release of silica dust. A large amount of proppant is delivered by pneumatic tankers. It is then blown into proppant storage containers. These storage devices can be pre-filled with proppant, either by dumping proppant into storage devices, or pneumatically conducting proppant to the storage devices, and then delivered to a well site for fracking. Once on the well site, various storage containers have openings in the top which allow air flow to the atmosphere. The flow of air creates a large dust cloud formed of silica dust, which blows out of access doors. This especially risks being a problem for workers who are looking into the interior of a storage container to monitor the appropriate fill level. As proppant is dispensed from the storage device, additional silica dust is produced and released. As the proppant is dumped into a blender, further silica dust is produced and released. As a result, dust often is produced and released at many different stages of the process at a well site.
During this process, if workers are at the well site, they also often stand near or directly in the path of a cloud of airborne silica dust. If workers inhale these small particles of silica dust, the each worker risks particles being embedded deeply into the tiny alveolar sacs and ducts in the worker's lungs, where oxygen and carbon dioxide gases are exchanged. The lungs may not be able to clear out the embedded dust by mucus or coughing. Substantial and concentrated exposure to silica dust therefore risks leading to silicosis.